Problem: Expand.
We expand the parentheses using the distributive property : $ A(B+C)= A\cdot B+ A\cdot C$ We can also think about the problem using an area model: $w^2$ $-9$ $-4w$ Here's how the solution goes, algebraically: $\begin{aligned} &\phantom{=}{-4w}(w^2-9) \\\\ &={-4w}(w^2)+({-4w})(-9) \\\\ &=-4w^3+36w \end{aligned}$ Here's how the solution looks in terms of the area model: $-4w^3$ $36w$ $w^2$ $-9$ $-4w$ In conclusion, $-4w(w^2-9)=-4w^3+36w$